Translation:If I ate more, I would be stronger.
אני לא בטוח לגמרי כי אני לא גר בישראל, אבל מרפיקס אומר שזה "תקוות שווא".
Literally "Futile Hope".
What is the difference with: If I would have eaten more, I would have gotten stronger.
I do not believe Hebrew has the "would have" tense. I think the sentence you are suggesting fits but is not as literal.
I think actually this is the more correct translation of the sentence (if you omit the first "would"); לו implies an impossible action, corresponding to the conditional 3 in english, while אם can take both translations equally following the context.
Franzisca, You can't omit the first "would" or it will be ungrammatical. Also, לו indicates subjunctive mood, and not an impossible action. You are correct though, that אם can be either subjunctive or indicative.
I am not completely sure what subjunctive means, I am only recalling Duos introduction saying that לו "are used only for events that haven't or can't happen". And in english conditionals the if-part doesnt come with "would", so you need to omit it as in "If I had eaten more,..."
Lu is for things that can't happen OR for things that are wished for, hoped for, or theoretical.
Indicative: I was rich.
Subjunctive: If I were rich.
(notice how the verb changes form in English? The first one is said as a fact. The second one is a hope or wish.)